Polyesters obtained by a polycondensation reaction between a diol and a dicarboxylic acid are widely used in various uses such as fibers, films and bottles because of their excellent properties. 1,4-butanediol (hereinafter also referred to as “1,4-BDO”) is used as a material to produce polybutylene terephthalate (hereinafter also referred to as “PBT”) by polymerization with terephthalic acid, and as a material to produce polybutylene succinate (hereinafter also referred to as “PBS”) by polymerization with succinic acid. Since PBT has excellent moldability, heat resistance, mechanical properties and chemical resistance, polyesters are widely used not only as materials for molding electric parts and automobile parts, but also as fibers having a soft texture and stretch properties. Further, PBS is also expected as a biodegradable material attaining biodegradation of used molded articles and attaining composting.
Known industrial methods of producing 1,4-butanediol which is a constituent component of PBT and PBS include a method wherein acetylene and formaldehyde are reacted and then the reaction product is hydrogenated; and a method wherein butadiene is reacted with acetic acid in the presence of palladium catalyst to yield a 1,4-diacetoxy product, and the product is then subjected to reduction and hydrolysis. Further, in recent years, due to the concern about the rise of the price or depletion of petroleum, methods of producing a monomer originated from a biomass resource are attracting attention. Known methods of producing 1,4-butanediol originated from a biomass resource include a method wherein 1,4-butanediol is directly obtained by fermentation; and a method wherein succinic acid obtained by a fermentation method is reduced by hydrogenation to indirectly obtain 1,4-butanediol.
As a purification method of 1,4-butanediol, distillation is known. However, the problems per se of the by-production of THF during the production of polyesters, and of the extension of polymerization time were not reported. U.S. Pat. No. 4,154,970 B discloses a method wherein butanediol generated by ester exchange in the polymerization of PBT is distilled after adding thereto a base such as alkaline metal alcoholate; and U.S. Pat. No. 6,387,224 B discloses a method wherein the 1,4-butanediol mixture obtained by hydrogenation of a maleic acid derivative is distilled after adding an alkaline substance to obtain 1,4-butanediol with small contents of specific impurities. However, the 1,4-butanediol described in those publications is not originated from microbial fermentation, and they are silent about the problems of by-production of THF during production of polyester and of the extension of polymerization time. JP 2013-32350 A discloses a method of obtaining purified 1,4-butanediol having decreased impurities wherein a crude 1,4-butanediol originated from a fermentation broth, which contains as an impurity 2-(hydroxybuthoxy)-tetrahydrofuran, is heated in the presence of an amine. However, JP '350 is silent about 1) an alkaline substance other than an amine and 2) extension of the polymerization time during production of the polyester when the 1,4-butanediol originated from a fermentation broth is used. Further, JP 2010-150248 A discloses a method wherein a 1,4-butanediol-containing solution (not an actual fermentation broth) is treated with a nanofiltration membrane to remove impurities such as inorganic salts, saccharides and proteins to improve the distillation yield. However, those publications are silent about the problems of by-production of THF during the production of polyester and of the extension of polymerization time. WO 2010/141780 A discloses, among other things, methods of purifying 1,4-butanediol.
We discovered problems in using 1,4-butanediol originated from microbial fermentation from which the removal of the impurities is insufficient as a material to produce a polyester, which problems are that THF is by-produced, and the polymerization time is greatly extended when compared to 1,4-butanediol originated from petroleum.
Accordingly, it could be helpful to provide a process of producing 1,4-butanediol suited for a material of producing polyesters, by which process by-production of THF during the esterification reaction of 1,4-butanediol is reduced and the extension of polymerization time is reduced even though the 1,4-butanediol originates from a fermentation broth.